A disturbing video — now viral — shows the April 29 crash of a Boeing 747-400 freighter at Afghanistan’s Bagram airfield.

Attempting to take off near a thunderstorm, the big, Dubai-bound plane stumbled to a height of 1,312 feet, according to an Afghan official quoted in press reports, and then lurched downward to fiery extinction, killing its seven American civilian crew members. The aircraft carried five, 16-ton military vehicles called mine-resistant, armor-protected vehicles, or MRAPs. It had flown 330 miles from Camp Bastion to Bagram with this weighty payload but with less fuel, meaning the aircraft weighed less.

It’s important to stress no cause for the crash has been announced. But the tragedy raises questions.

Mine come from perspective of the author of a book about the 747-400 — now out of print — and longtime observer of the Air Force and civilian contractors.

1. Why are contractors performing a strategic airlift mission? The Air Force’s strategic airlift fleet is the only part of inventory that isn’t long in the tooth. We have 223 relatively youthful C-17 Globemaster IIIs, plus the C-5 Galaxy. Why farm out this military mission?

2. Why are planes carrying MRAPs? If you wanted, an M1A2 Abrams main battle tank could be loaded aboard a C-5M Galaxy and hauled across an ocean. It isn’t done because it’s uneconomical. Heavy vehicles abound by the thousand. According to a service news release, the Marine Corps alone has 1,200 MRAPs in Afghanistan where U.S. forces are withdrawing. That’s enough for 240 costly, labor-intensive flights in a 747-400. Heavy vehicles should travel by sea.

3. Why is a 747-400 carrying MRAPs? Unlike a C-5 or C-17, the 747-400 doesn’t have roll-on, roll-off capability. If a plane were to carry heavy vehicles it should be designed for that purpose.

4. Who loaded the cargo? This is the big one. Aerial port specialists and loadmasters would be pivotal for Air Force cargo. Sources say in this case the contractor had responsibility. The public deserves to know who tied down those MRAPs in the fuselage and how much training that person or persons received. Again, no cause for the crash has been announced but a sudden shift of cargo, upsetting the plane’s center of gravity and rendering it unable to climb out from Bagram, is the almost-certain culprit. It’s fair to ask who measured weight and balance, loaded the plane, and did the tiedown.

See a discussion of these issues at the Military Times Forums: airforcetimes.com/cargo.

The loss of seven Americans is tragic. The sight of a majestic aircraft falling from the sky tore at my heart.

Our sorrow should not prevent us from asking why contractors were assigned a military mission and whether contractors can be reduced once our troops leave Afghanistan.■